Because “medium hot” is largely a factor of personal taste (people perceive spice differently based on their dietary habits and taste buds) and the final heat of a hot sauce will vary with a recipe, it’s hard for us to recommend chilies that will give you exactly the result you’re looking for.

You might consider experimenting with a blend of a small number of medium dried chilies or hot dried chilies for heat and a larger amount of mild chilies (which tend to be fruitier) for flavor. Tweak the balance in your recipe until you get the result you like.